1. Field of the Invention
The invention relates to a method for controlling the power supplied from an AC power supply to an ohmic load, the AC power supply providing a sinusoidal output, the method comprising connecting the load to the AC power supply during a part of each period of the sinusoidal output, wherein the power supplied from the AC power supply to the load is varied by varying the duration of that part of each period. The invention further relates an apparatus for controlling the power supplied from an AC power supply to an ohmic load, comprising a switch for connecting the load to the AC power supply, and a controller for providing a control signal to the switch.
2. Discussion of the Related Art
U.S. Pat. No. 6,114,669 is directed to a method and apparatus for controlling power to a load, wherein a controller operates according to a so-called phasecut control method. Within each half period of the AC voltage, a switch is closed for connecting the load to an AC power supply and at a zero-cross of the AC voltage, the switch opens again. In this known apparatus, flicker and interference radiation are reduced by varying the phase angle of the control signal around a phase angle corresponding to the power to be provided.
Although the known apparatus allows the load to be gradually connected to the AC power supply, a phasecut control method shows the disadvantage that the control steps are relatively large, whereas phase cutting is inaccurate at small phase angles in particular. Moreover, the phasecut control method causes harmonic distortion resulting in a relatively low value of the power factor.